Lamp having light diffusing envelope

ABSTRACT

An incandescent lamp has an envelope made of partially crystallized glass in order to diffuse the light emanating from the filament.

United States Patent 1191 Chu 1451 May 20, 1975 LAMP HAVING LIGHT DIFFUSING 2,017,733 10/1935 Sakakura et a1 313/116 x 2,073,237 3/1937 Yajima 313/116 X ENVELOPE 3,238,085 3/1966 Hayami..... [75] Inventor: Gordon P. K. Chu, Danvers, Mass. 3,3 3.54 1/1963 Johnson 3,368,712 2/1968 Sanford et a1. [73] Ass'gnee' GTE lncm'pmated 3,504,319 4/1970 Veres 22012.1 R Danvers- Mass- 3,625,718 12/1971 Petticrew [06/39 DV [22] Filed: Sept. 20, 1973 [21] Appl. No.: 399,100 Primary Examiner-A1fred L. Brody Attorney, Agent, or Firm-James Theodosopoulos [52] US. Cl. 313/116; 106/39.7; 106/54; 117/97 [51 1m. (:1. H0lk l/26; HOlk 1/28 ABSTRACT [58] Field of Search 313/116, 110, 112;

06/39 Dv 54, 39]; 220/2 l R; 7/97 An incandescent lamp has an envelope made of partially crystallized glass in order to diffuse the light em- [56] References (med anating from the filament.

UNITED STATES PATENTS 6/1932 Hageman et a1 313/112 1 Claim, 1 Drawing Figure 1 LAMP HAVING LIGHT DIFFUSING ENVELOPE DESCRIPTION OF THE PRIOR ART Incandescent lamps generally have a light diffusing envelope in order to eliminate the harsh glare of an incandescent filament. In inside frost lamps, the envelope is made light diffusing by etching the inner surface of the lamp envelope with hydrofluoric acid, as disclosed in US. Pat. No. 1,687,510.

Because of the large number of incandescent lamps manufactured annually, in the millions, large quantities of acid are used in etching. resulting in considerable discharge of acid fumes into the atmosphere.

As concern for the ecological effect of manufacturing processes on the environment has been heightened in the past few years, it has become desirable to dispense with acid etching as a method of making light diffusing envelopes.

Accordingly, it is an object of this invention to provide a light diffusing envelope that dispenses with the need of acid etching.

SUMMARY OF THE INVENTION An incandescent lamp in accordance with this invention has an envelope that is made of uniformly partially crystallized glass. The glass is not transparent but translucent, i.e. light diffusing, and is efficient in the transmission of visible light therethrough. Moreover, the crystallized glass is readily workable so that it can be sealed to the flare of the usual glass stem press at the base of the lamp.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE in the drawing is an elevational view, partly in section, of an incandescent lamp in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, an incandescent lamp in ac cordance with this invention comprises a crystallized glass envelope 1 which can contain a gaseous filling such as nitrogen and argon. The bottom of envelope 1 is sealed to flare 2 of the usual stem press glass mount 10. Lead-in wires 3 extend through and are supported by stem press 4 of glass mount 10. A coiled tungsten filament 5 is supported between the upper ends of lead-in wires 3. Lead-in wires 3 extend downward between tipped off exhaust tube 6 and flare 2. One of the lead-in wires is connected to center contact 7 of the usual screw base 8 which is fastened to the bottom of envelope I, while the other lead-in wire is connected to the rim of base 8.

The glass envelope was made from a glass having the following composition, by weight:

up 1348% l??? 1'33 sfo 70:71 A120" 6.10 CaO 0.52 MgO 0.18 3,03 1.02 50, 2.90

The raw materials providing these oxide ingredients were mixed and heated in a refractory tank or container at 1350 to 1400C for 3 to 8 hours to form uniformly melted glass from which lamp envelopes were formed. At this stage the glass envelopes were transpar ent, having a light transmission of about 99%. The glass envelopes were then nucleated and crystallized by heating under a controlled schedule at a rate of 15 to 20C per minute. In order to obtain uniform finely dispersed nucleation and crystallization, crystallization was carried out in two stages. First, the envelopes were maintained at a temperature of 500565C for about 10 minutes. This first stage crystallization temperature range is about 50C above the lower annealing temperature (475500C) of the glass. The heating was then continued to a temperature of 750-785C which was maintained for 10 minutes. This second stage crystallization yields more complete crystallization. This process yielded envelopes having a light transmission of about 95% and which were sufficiently light diffusing to eliminate the harsh glare of an incandescent filament. More extensive crystallization could be obtained, for example, by more extensive second stage crystallization, such as at 770-800C for 20 minutes. This yields a light diffusing envelope having a light transmission of about 92% and in which the incandescent filament is not discernible through the lamp envelope.

After envelope 1 was crystallized, it was still sufficiently workable so that it could be readily sealed to stem press glass mount 10. Mount 10 is usually made ofGl2 glass, which is a low temperature, soft, high lead glass, most suitable for sealing dumet wire 11 which is part of lead-in wire 3.

Crystallizable glasses suitable for lamp envelopes of this invention have a composition within the following limits: Li O 8 to 20%; Na O and/or K 0 1 to 7%; SiO 45 to 72%; M 0 4 to 20%; C210 and/or SrO and/or BaO and/or MgO 0.6 to 7%; B 0 1 to 4%", As O and/or Sb O and/or P 0 and/or M00 2 to 7%. The nucleation and crystallization temperature of these glasses is about 520 to 820C, which process changes the glass from transparent to translucent, but having high efficiency of light transmission, say, at least about The nucleation temperature is between about 520 to 560C. This means that if a lamp envelope is formed directly from the hot glass melt, the envelope must be cooled to the nucleation temperature, or preferably below said temperature, before it is reheated to the crystallization temperature.

I claim:

1. An incandescent lamp comprising a filament disposed within a light diffusing uniformly crystallized glass envelope, the entire envelope being crystallized, which is sealed at its lower end to the flare of a stern press glass mount, the envelope having a high efficiency of light transmission, the glass composition of said envelope being as follows:

U0 8 to 20% Na O and/or K 0 l to 7% Si0 45 to 72% Al O 4 to 20% C210 and/or SrO and/or BaO and/or MgO 0.6 to 7% B 0 1 to 4% A5 0 and/or Sb O,- and/or P 0 and/or M00 2 to 7%, 

1. AN INCENDENSENT LAMP COMPRISING A FILAMENT DISPOSED WITHIN A LIGHT DIFFUSING UNIFORMLY CRYSTALLIZD GLASS ENVELOPE, THE ENTIRE ENVELOPE BEING CRYSTALIZED, WHICH IS SEALED AT ITS LOWER END TO THE FLARE OF A STEM PRESS GLASS MOUNT, THE ENVELOPE HAVING A HIGH EFFICIENCY OF LIGHT TRANSMISSION, THE GLASS COMPOSITION OF SAID ENVELOPE BEING AS FOLLOWS: LIO2 N TO 20% NA2O AND/OR K2O 1 TO 70% SIO2 45 TO 72% AL2O3 4 TO 20% CAO AND/OR SRO AND/OR BAO AND/OR MGO 0.6 TO 7% BEO3 1 TO 4% AS2O3 AND/OOR SB2O3 AND/OR P2O5 AND/OR MOO3 2 TO 7%. 